In prior art processes for the production of deep fried potato products, the potato doughs are generally prepared by mixing dehydrated potato solids or solid mixtures with water, using prolonged and vigorous agitation to ensure that the water is uniformly distributed throughout the mixture. Such prolonged agitation generally results in a destruction of potato cells, producing ruptured cells and free starch solids. The presence of these substances and especially that of free starch solids results in a dough which is excessively cohesive and tacky. When such doughs are used to prepare French-fried potato products, the resulting product has a gummy, only semi-mealy interior and a tough exterior skin and is consequently, inferior to an ideal French fry produced from raw potato pieces - if the doughs are used to prepare potato chips, destruction of the potato cells is less important as concerns the quality of the finished product; however, difficulty in dispersing the solids uniformly so that a lump free mixture is obtained, is encountered in either case.
In these prior art processes, the potato doughs can be prepared by either the addition of solids to water or vice versa. The types of mixing equipment used to prepare the potato dough are ribbon mixers, paddle mixers or sigma blade mixers, etc. One mixing technique which has been described, is to carry out mixing in a Hobart mixer a type of vertical, planetary action mixer manufactured by the Hobart Machine Company for only 2-3 minutes at relatively low speed to avoid destruction of the mealy character in the finished French fries.
When mixing is carried out by any of these prior art processes it is found that it is difficult to distribute water evenly throughout the mixture, since the dehydrated potato particles first contacted by the water are converted to a thickened dough and further migration of water is prevented so that dry areas are created. Moreover, in the case of French-fried products, as mixing is continued in an attempt to distribute water from areas which contain relatively too much water to areas which are dry, the potato cells are ruptured and the mealy character of the French fries produced from such doughs is partially destroyed.
These aforementioned problems are not encountered when water is combined with potato solids in an amount equal to or greater than the absorption or hydration capacity of the solids, such as in the case of mashed potato preparation. The absorption or hydration capacity of the potato solids as determined by any one of a number of standard methods (for example, AACC Method 56-20) is generally greater than 3-5 pts water/1 pt. potato solids. This amount of water is equivalent to that required for complete hydration and swelling of the potato solids to a point where free or excess water is present in the mixture and this excess water coats the potato particles of the mixture to form a continuous aqueous phase. Consequently, the apparent viscosity of such mixtures is relatively low, the potato particles are free to migrate within the continuous aqueous phase, and reconstitution of the dehydrated potato solids can be acomplished with little or no mixing.
In contrast, when a potato dough suitable for deep-fried potato products is prepared, the amount of water used is generally less than the absorption or hydration capacity of the potato solids and is of the order 11/2 -21/2 pts. water/ 1 pt. potato solids. Consequently, no excess water is present in these mixtures, a continuous aqueous phase is not formed and the apparent viscosity of these mixtures is relatively high since the material forms a rigid dough upon complete absorption of all the water present by the potato particles. When mixing of these doughs is carried out, the shear stresses created are much greater than when excess water is present and the potato granules are more susceptible to breakdown under prolonged agitation.
A further disadvantage of these mixing processes is that they do not allow for the continuous production of potato dough from dehydrated potato solids. Most techniques described are batch processes, so that the dough must be transferred to an extrusion or shaping operation in a second step. In addition, if the dough is allowed to stand for long periods of time, aging processes may occur, thereby altering the texture of the products prepared from such doughs.
After the potato solids have been rehydrated, they are shaped into pieces suitable for deep-frying, by extrusion or sheeting. In a typical extrusion operation, the dough is fed to a barrel-type extruder, which consists of a screw conveyor and an orifice plate or die fitted to the end of the barrel. The screw conveyor rotates to provide the necessary pressure to convey material through the barrel and to force it through the orifice. The holes in the orifice plate can be of varying dimensions so that a wide variety of shapes is possible. For example, rectangular or cylindrical dough pieces can be produced by using square or circular shaped holes, or a continuous ribbon or sheet can be produced by using an elongated rectangular slot. Once the dough pieces are extruded, they can be cut off to the desired length using a mechanical cutter.
A disadvantage of the extrusion method is that relatively high shear forces are generated during extrusion of the dough, owing to its relatively high viscosity. Consequently, further destruction of potato cells takes place, (in addition to that caused by over-mixing), so that a product of inferior quality results.
In a typical sheeting operation, the potato dough is passed between successive pairs of rollers, which squeeze the dough into a progressively thinner sheet. For example, a first pair of rollers might be used to give a sheet of 2 inch thickness; a second pair would then reduce the 2 inch sheet to 1 inch, and a third pair would reduce the 1 inch sheet to 1/2 inch, etc., until the desired thickness is reached. The final sheet would then be trimmed and cut into pieces suitable for deep-frying.
The sheeting method possesses the advantage over the extrusion method, in that it does less work on the product in terms of shear. However, its disadvantages are that the doughs may have a tendency to stick to the rollers, that the edges of the sheet are invariably frayed, (especially in the case of a mealy non-cohesive French-fry dough) so that trimming and recycling are required, and that a relatively long sheeting line may be required (in comparison to the compactness of a short extruder).
Many processes employ one or the other of these operations to shape or form the potato dough, and sometimes both may be used in combination, for example, extrusion into cylindrical slabs, followed by sheeting into thin wafers, such as in the case of potato chips.
It can be seen from the preceding discussion of prior art processes, that existing rehydration and shaping methods do not provide a fully containuous method of preparing deep-fried potato products, such as French-fries and potato chips; that the mixing and shaping operations are not essentially trouble-free, and that the products produced by these methods are not completely satisfactory as regards texture and eating qualities.